Electrical measuring system



Sept. 2, 1952 A. B. JAcoBsl-:N

ELECTRICAL MEASURING SYSTEM 3 Sheets-Sheet l Filed March 22, 1945 A TTOP/VEY Sept. 2, 1952 A. B. JACOBSEN 2,609,533

` ELECTRICAL MEASURING SYSTEM Filecl March 22, 1945 l 3 Sheets-Sheet 2 Fl G. 2 FIG. 3

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ANDREW B. JA COBSEN A TTOR/VEV Sept 2, 1952 A. B. JAcoBsEN ELECTRICAL MEASURING SYSTEM 5 Sheets-Sheet 3 Filed March 22, 1945 INVENTOR.

3 1 n m@ I m O IIIIIIIII1||| 1 m n l= D .Ulwm Imm m 2 5 vwl |ml m B 0 C m R m m N A ATTORNEY jatenteci Sept.. 2, 1952 V ELECTRICAL MEASURING SYSTEM Andrew B.".lac`obsen, Somerville, Mass., assignor, by mesne assignments, to the United States of America asrepresented by the Secretary of War application March 22, 1945, siariiatsilzss This invention relates generally to an electrical `circuit and more particularly to a circuit for decoding`V received radio frequency pulsesand for determining the range of the apparatus emitting said pulses.

In one type of navigational system, a beacon, usually in a fixed location, is interrogated by radio pulses from a` shpborne or airborne interrogating device. On being interrogated, the beacon transmits a coded series of radio pulses. The interrogating ship or plane carries a respondingdevice `which will respond only to the code of a preselected beacon and will indicate the range of said beacon. f'the interrogating device transmits a directional beam of radio energy, the azimuth of the beacon withv respect to the interrogatormay'also be determined by conventional methods.

One object of this invention is to provide a circuit which will respond only to a series of pulses arranged in a predetermined code and which will indicate the range of the responding beacon.Hy It is also an object of this invention to provide a continuous indication of said range although the beacon is triggered intermittently.

Other objects of my invention will become apparent from the following description taken in connection with the accompanying drawing in which:

Fig. 1` is a block diagram of a circuit embodying the principles of this invention;

Fig. 2 is a diagramof a pulse stretcher circuit;

Fig. 3 is a diagram of a differential error circuit;`

Fig. Il is a diagram of a connector circuit;

Fig. 5 is a diagram of a memory circuit; and

Fig. 6 shows a group of curves illustrating the operation of the invention.

Referring now more particularly to Fig. 1, rectangular wave generator Ill is supplied with an input fromthe transmitter (not shown) which transmits a radio pulse to interrogate the xed beacon. Generator lll produces a rectangular Wave, the width of which is determined by a bias supplied from memory circuit 23 to be described subsequently. lSuch rectangular wave-generators are well known to those skilled in the art. an example being described on pages 176 and 177 of Ultra-High Frequency Techniques written by Brainerd, Koehler, Reich, and Woodrui, published by D. Van Nostrand Co., Inc., in July of 1942.

Another rectangular wave generator for producing a rectangular wave, the width of which is phantastron. This circuit comprises a pentagrid 5 Claims. (Cl. 343-13) a 2 tube connected so that its operation is very similar to a "cathode` coupled multivibrator, the plate section of Asaid tube being the normally off tube while theA screen grid section is normally the on tube A condenser is placed in the plate circuit of said tube and is caused to discharge linearly, enabling theI duration of the resulting pulse to be varied in proportion to changes of applied control voltage. The phantastron circuit is fully set forth in Massachusetts Institute of Technology Radiation Laboratory Report No. 63-21, dated August 21, 1943, written by Kelner, Hughes, Berg, Hinkle, and Chance, and entitled An Adaptation of the Phantastron Delay Multivibrator Circuit to the SSAT Tube.

The output of generator Hi is supplied t0 trigger pulse generator il which may be a conventional dilerentia'ting circuit. The output of generator ll is supplied to gate generator I l which produces square waves, rectangular wave generator 5i), and rectangular wave .generator 55, all of which may lbe similar in construction to generator i6. The output of generator l is applied to coincidence circuit I6 and also to coincidence circuit ll through delay circuit l5. Delay circuit l5 is a conventional delay network, the midpoint of which is tapped to supply a range marker pip to output I2 which may be used to indicate range on a cathode ray tube. Circuits I6 `and Il are also supplied with a video signal which is received from the iixed beacon as a result of the interrogation. Circuits I6 and ll are conventional coincidence circuits which will not permit passage of the video signal unless a gate pulse occurs simultaneously therewith. Such circuits are conventional and may consist of electron Vtubes so biased that either video or gate pulse separately will not permit an increase in plate current but when they occur simultaneously such action takes place.

The outputs of coincidence circuits Iii and l1 are applied to pulse Stretcher circuits I8 and I9 respectively. Pulse stretcher circuits I8 and I9 serve to widen the output from circuits I 'and Il.

Fig. 2 shows a circuit which can be used for pulse stretcher circuits I8 and I9. In Fig. 2, a negative pulse applied between terminals 25 and 2t will charge the capacitor 21 rapidly as tube 28 will conductlcurrent in this direction. When the pulseis removed, condenser 21 discharges through resistor 29 which has a large amount of resistance. Thus, the time required for discharge is longer than the time required for charge and a widened pulse is produced between terminals 30 and 3|.

Referring now to Fig. 1, the outputs of circuits I8 and I9 are applied to differential error circuit 20. Fig. 3 shows a circuit which may be used as the differential error circuit 20. In the circuit of Fig. 3, the initial conditions are such that electron tubes 39 and 40 are not conducting current. If a pulse is applied across terminals 35 andA 36,and if a pulse of approximate equal amplitudebut of different widthis applied across terminals 31 and 38, more current will attempt to flow through one of electron tubes 39 and III) than through the other, thus creating a voltage to beused as an output. Capacitor 4I- serves-to' by-pass short pulses comingfromfpulsexstretcher circuit I8.

The output of differential error circuit 2U is applied to connector circuits v2.l.and 22connected` in series. Connector circuits 2l `and 22 may consist of circuits similar to that shown in Fig. 4. In Fig. 4, electron tube 60 is connected back to back Awith tube 6I thecathode -of each tube beingconnected to the plate-of the other. A-commoninput connection from the error circuit or connector circuit 2|is provided at20A. Energizing potentials `for the connectorv or clamping. circuit are available from the respectiveV preceding circuit, such as the error circuit 20; Between the cathode and the grid-of tube 60, thereis provided a sourceof D.C. potential 62 in series with resistor 64 and secondary winding 68 of transformer 59. Between the cathode and `grid of tube 6I is similarly connected a source of D.C. potential 63,

resistor 65 and secondary winding.61of .transformer 59A. Tubes-ISI)v land 6Iv are consequently biased to cutoff unless a pulse is supplied to their grids through transformer 59A, from-a gate generator, as at 54 permitting them to conduct and enabling current to liow in eitherdirection. The output terminal of the circuit is indicated atg22A which may be connected to the-connector 22. or

to the memory circuit 23.

The output of connector` 22-isappliedto Amemory circuit 23. This circuit may be constructed as set forth in Fig. 5. In Fig. 5, the signal or error voltage is applied to terminalr68 and, during the duration of said error voltage, capacitors 6'9 and 10 charge with the charging Acurrent flowing through resistor 1I. The chargeon capacitor'69, serving as biasfor electron tubef12,contr,ols .the amount of plate current iiowing through this tube and thus the amount of; current through resistor 13. When the potentialat'the end of resistor 13 connected. to resistor 1.4-rises.above the charge on capacitor 10, current iows through-.resistor 14 to increase the chargeoncapacitor. 10. Connected to the plate of tube 12 is shown a source of voltage15. Switches 16,111, and.18,are mechanically connected' together 'andi represent a single throw triple-pole device which is normally open but when closed .permitslmanual setting of the bias byv moving the sliding. contact on potentiometer 19 which hasconnectedacross it sources of voltage 80..and 8l The manner in whichA memory circuit 23 operates may be explained with reference to Fig. 5. The voltage chargeacrosscapacitor 6.91isproportional to the error voltage. `Iffthisisa large-voltage, tube- 12 conducts more readily andthe potential at terminal 82` will rise rapidly. Thel potential at .terminal 82rises orfalls'in an,v exponential manner due to .thecharge or` discharge of capacitor. 10'. The gridof tube 12: rises with the cathode .as .the grid is connected to the cathode by resistors 1 I and 14.v andcapacitor; 69.

Thus, it willbe seenthatza positive-errorvoltf age appliedat.` terminal will'- produce anoutput voltage at terminal 82, said output voltage icreasing at a rate depending on the magnitude of the error voltage. A negative error signal at terminal '62 will produce a similarly decreasing output voltage. Said increase or decrease in output voltage will continue for a time long compared to the interrogation period.

f Whenswitches 16, 11,:and 18 are closed, resistor 14 is shorted and it is possible to control the voltage at terminal 82 by regulating potentiometer 19. Switch 11 prevents power loss from sources and 8l when potentiometer 19 is not beingused.Theoutput of memory circuit 23 is applied-tothe range indicator 24 and also to adgjust..the biasv of rectangular wave generator I0.

l `The output of rectangular wave generator 50 is `applied lto trigger pulse generator 5I, the output of whichis applied to gate generator 52. The output of gate generator 52 is applied, along with the video signal, to coincidence circuit 53, the output of which is appliedV to gate generator circuit 54. Rectangular. Wave generator 5.0, trigger pulse generator 5I, gate generator 5.2', coincidence circuit 53, and gate generator 54 are'respectively similar in. construction. and operation to' 'riectangularV wavegenerator. I0, trigger pulsegenerator, II, gate generator --I'4,v coincidence circuit I6 4and v.gate .generator I4 described above. "Reef tangular wave generatorV 55, trigger pulse l. generator56, gate .generator 51, coincidencecircuit 5.8, andgate generator 5.91arefsimilar. in construc- .tion.andfoperation tothe corresponding'l components 5II-54 `describedabove.,The outputs oflgate generatory 54 ,and 59... are appliedtoconnector cir.- cuits Z-Land 22` respectively. AInfthe explanation of the .operationuof this invention, .referenceewill be made to the curves in Fig. 6.

The interrogatingpulse from the airborne.l or shipborne transmitter isshown as 88 in- Fig. 6A. The xed beacon on being interrogated transmits code pulses Y 81|', 82 and 8-3, the distance vbetween these: pulses ,being arranged in vaccordance l. with ,a l predetermined code.- Pulse .80.- on :being .applied to f generator I 0' initiates fthe .production .of z rec.- tangularwave 84shown in-Fig. 6B;- Thefwidth of thiswave isy adjustedbyfthe biassuppliedffrom memory` circuit: 23 to be: somewhat less'. in., duraition than the interval between pulses 88 andgSI; The application of rectangularwave .to trigger pulse generator: I l Aresults-1.infthefproductionzof trigger 'pulses 8.51-and '86,;.asgshownfinz Fig.v 6C. Pulseffisineffective to operatenarrowxgatefgenerator I4 but pulse 88, of opposite polarity,.op: eratjesznarrovv` gategenerator Mito produce pulse 81 of'Fig. 6D. Pulse 81.isxappliedto delay circuit I51toyproduce delayed pulse88jalso1sho`wn inzFig. 6D. Pulses 81 and 88 along iwith @thevideo-signal containing `:pulses 80,8I; 8.2i, and 83 are applied to coincidence; circuits Iz6 and I1. .If .pulseeBYI falls vmidway. between-.pulses81v and 88'.'- theuoute puts .ofi coincidence circuits |31. and;` I1' will lbe equal, resulting. ,in no verror voltagebeing.V producedby differentialerror circuit20L1'If pulse 8l. .coincides more-nearly with.` one Vof the two 'pulses 81'f`-88'than withthe other, alarger 1p1-ilse will fbe producedby.one-iof1the:tvvo pulse stretcher circuits, I8 .or`l9, than isproduced ^by the otl-ierf These unequal outputsv are applied to thefcircuit 20, resulting Ain, theproductionbfa differential errorvoltage, similar to pulse shown iniligfGF.

The center point of delay network I5 is tapped .to provide Aa range marker pip 8.9, shownin-.Eig 6E,Amidway between pulses r8'1-and 88'.: This'pip beacon..

'acoatee Pulse generated by circuit Il has .noie'iect on generator i! and 55,1butpulse 36` ofopposite' polarity causes generator 4-andi to produce pulsesl and 92, as shown -in Figs. 6G and 6J respectively. The lengths of pulses 9| and S2 are preset to be equal to the interval between pulses 8l and 82 and Vbetween lA and 83 respectively. Trigger pulse generatore! and gate generator 52 operate to produce a pulse 93 shown in Fig. 6H at the trailing edge of pulse Si. Pulse 93 along with thevideo signal received from the iixed beacon is applied to coincidence circuit 53. If pulse 82 coincides with pulse 93, a pulse is applied to gate generator Y5d which produces la somewhat larger pulse, shown at 94 in Fig. 6I. Pulse 5M is applied r to connector circuit.V 2l rendering that circuit conductive tothe differentiarerror voltage developed by circuit 26. Pulse 92 through the action of trigger pulse generator 5S and gate generator 5l `produce gating pulse` 95, shown in Fig.\6K, at the `trailing edge of pulse 32;Y When pulse 83 and 95 coincide, a pulseis applied to generator 5S which produces l a somewhat! longer pulse, as shown at 96 in Fig."6L.' Pulse 96 is applied to connector circuit 2Q which is rendered conductive to allow the error voltage developed by differential error signal to pass to memory circuit 23.

Memory circuit E3 produces a voltage 'wave indicative of the range to the fixed beacon. This range Voltage varies in accordance with the error voltage generated by circuit 26. If the beacon is interrogated intermittently, memory circuit 23 develops a voltage between the coded replies, said voltage being indicative of the range determined by the last reply.

Referring to Fig. 5, the rate at `which capacitor 'i0 changes its charge is proportional to the velocity of the moving interrogator with respect to the beacon. The time constant of the circuit containing capacitor 'l0 is approximately equal or larger than the longest time interval between successive appearances of the video signal permitting capacitor 'm to change its voltage; thus, changing the bias on wave generator IU in relation to the rate of change of the distance between the interrogator and the fixed beacon which results in velocity memory. If the rate of change of the distance between nterrogator and the .beacon remains constant, the memory circuit will anticipate the change in distance between successive interrogations and position pulses 8l and 88 so that pulse 8| falls between them.

Referring to Fig. 5, it will be noted that when switches 1E, l?, and 'I8 are closed the position of pulses 87 and 88 may be controlled manually as the voltage at terminal 82 may be varied, thus ,permitting the beacon to Ibe searched for and, after finding the beacon, upon proper positioning of gates 87 and 83, opening switches 1t, l1, and 78 will permit the beacon to be tracked automatically.

Consideration or Fig. l as above described will disclose that the primary circuit arrangement is what may be termed a closed loop range tracking circuit. This closed loop circuit is comprised of a delay portion for the reference pulse, the

units IB and il, a gating and mixing portion where the coded sequence of reply pulses or video signal is introduced, the units lil, I6, i8 and l5, il, le, the error signal portion 20, two connector circuits 2l and 22 and the memory circuit portion 23, an output of which is coupled back to an input of unit i@ thi/1S completing the loop.

-1 4The connector means 2l and 22 may be termed disablingY or enablingmeans interposed between YZI'andZB..V c f i From-the above it will, be evident that in ace cordance with the presentzinvention there is dise closedfa system for continuously measuring at one station the distance to a particular one of apluralityof stations comprising at the onestation means for transmitting interrogating pulses at a regular repetition rate. Also provided are means for receiving reply pulses from any of the referred to stations, the reply pulses from each station comprising a differentcoded sequence of pulses recurrent at the repetition rate. Also provided are means for selectively tracking the reply pulses of the particular one of the stations to provide a potential representing the distance to that station. The selective tracking means comprise a closed loop tracking circuit responsive tothe first pulse of al sequence of-reply pulses. Alsorprovided are means interposed normally to disable the tracking circuit and means selectively responsive to the time spacing of the subsequent pulses,` of `a sequence for enabling the circuit and means for adjusting the time selectivity of the selectively responsive means to enable the circuit when the coded sequence of pulses forthe particular station are received. l

Y While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modications may be made therein without departing from the invention as set forth in the appended claims.

The invention claimed is:

1. In a device for continuously indicating the time of arrival of a series of pulses, means for indicating said time, means for predicting the time or the next arrival of said pulses, means arranged to measure the time of arrival of the first of said series with respect to the predicted time or arrival, rst and second means for connecting the measuring means with said indicating :and predicting means, means for causing the lirst connector means to be conductive if a second pulse arrives at a predetermined time after said first pulse, means for causing the second connector means to be conductive if a third pulse arrives at a predetermined time after said rst pulse, means for adjusting said measuring means and said predicting means in accordance with the predicted arrival.

2. A iirst means for producing a voltage varying in accordance with the time of arrival of a first pulse, the output of said first means being connected through iirst and second connector means to a utilizing circuit, means for causing the iirst connector means to pass said voltage if a second pulse arrives at a predetermined time after said iirst pulse, means for causing the seoond connector means to pass said voltage if a third pulse arrives at a predetermined time after said rst pulse.

3. A system for continuously measuring at one station the distance to a particular one of a plurality of stations comprising at said one station means for transmitting interrogating pulses at a regular repetition rate, means for receiving reply pulses from any of said stations, said reply pulses from each station comprising a different coded sequence of pulses recurrent at said rate, means for selectively tracking reply pulses of said particular one of said stations to provide a potential representing the distance to said station compris- 

